The SRK Science Thread 2.0

[pedoviejo]

negative universe means that the universe saddles.

iirc the shape of the universe implies how the universe will die.

[blitzfu]

Apparently the universe is indeed flat, with plenty of evidence to support it, primarily measurements of the Cosmic Microwave Background Radiation.
I’m not sure what exactly it means for the universe to be closed or open or flat, but watching videos of astrophysicist Lawrence Krauss is the closest I can come to grasping its meaning.

[forte95]

I’m not too sure, but I think I’ve read about two completely different things that reference the “shape” of the universe.

What we’re talking about right now is straight up geometry, just pure math of space. The root of it all is the postulate that goes “for a line l and a point p not on l, there exists exactly one line through p that is parallel to l”. Geometry with this postulate is “flat”; if there exists NO parallel through p, it’s “round”; if there exists infinitely many, it’s “hyperbolic”.

But I remember reading a discussion somewhere about the expansion of the universe (iirc, although lol what it seems like it’s barely related) that relates the “shape” of the universe to the critical density (really, REALLY not sure) but I don’t remember the exact discussion plus I don’t even remember what book I was reading. I’m looking through my e-books like mad trying to find that discussion. But I think what it says is that a flat universe is unstable equilibrium, meaning negative, gravitational pressure just barely balances the positive, outward pressure; round is too much gravitational pressure; hyperbolic is too much outward pressure. It’s what I remember, but it seems so unrelated, can anyone confirm?

EDIT: Also, different topic: apparently this happened in 2013, I only read about it now. It’s pretty interesting though.

A temperature below absolute zero

What is normal to most people in winter has so far been impossible in physics: a minus temperature. On the Celsius scale minus temperatures are only surprising in summer. On the absolute temperature scale, which is used by physicists and is also called the Kelvin scale, it is not possible to go below zero – at least not in the sense of getting colder than zero kelvin. According to the physical meaning of temperature, the temperature of a gas is determined by the chaotic movement of its particles – the colder the gas, the slower the particles. At zero kelvin (minus 273 degrees Celsius) the particles stop moving and all disorder disappears. Thus, nothing can be colder than absolute zero on the Kelvin scale. Physicists at the Ludwig-Maximilians University Munich and the Max Planck Institute of Quantum Optics in Garching have now created an atomic gas in the laboratory that nonetheless has negative Kelvin values. These negative absolute temperatures have several apparently absurd consequences: although the atoms in the gas attract each other and give rise to a negative pressure, the gas does not collapse – a behaviour that is also postulated for dark energy in cosmology. Supposedly impossible heat engines such as a combustion engine with a thermodynamic efficiency of over 100% can also be realised with the help of negative absolute temperatures.

In order to bring water to the boil, energy needs to be added. As the water heats up, the water molecules increase their kinetic energy over time and move faster and faster on average. Yet, the individual molecules possess different kinetic energies – from very slow to very fast. Low-energy states are more likely than high-energy states, i.e. only a few particles move really fast. In physics, this distribution is called the Boltzmann distribution. Physicists working with Ulrich Schneider and Immanuel Bloch have now realised a gas in which this distribution is precisely inverted: many particles possess high energies and only a few have low energies. This inversion of the energy distribution means that the particles have assumed a negative absolute temperature.

“The inverted Boltzmann distribution is the hallmark of negative absolute temperature; and this is what we have achieved,” says Ulrich Schneider. “Yet the gas is not colder than zero kelvin, but hotter,” as the physicist explains: “It is even hotter than at any positive temperature – the temperature scale simply does not end at infinity, but jumps to negative values instead.”

[MCP]

I remember reading about it. It was so cool how they were able to do it.

I really recommend reading the article.

[Wolfkiller]

Nasa Reveal New Impossible Engine

Edit: SRK sucks in the Dolphin phone browser, I’ve butchered the link… Hold on…
Edit again: Much better.

[MechWarrior]

Non-positive on the Kelvin meter?
What looks to be an engine that works just about entirely based on non-classical relativity/light having some mass, a little, but mass all the same?(shoutouts to Planck, IIRC, having the right idea since 1900, natch. Also, zero point physics fiends are creaming themselves at this one, this is a BIG deal)

…I’ll be dipped.

[forte95]

Nah man light doesn’t have mass, even in modern physics we’re sure of that, but it does have momentum. It’s why it can collide with particles and make them move differently + the light becomes different after collision because it lost momentum, like in the Compton effect.

Maybe the thruster has something to do with radiative pressure? But if it’s just bouncing microwaves around, why is there a net thrust? Shouldn’t the microwaves push the front end just as much as the rear end? I wanna see the design of that thing, how it actually looks inside, because this is very interesting. The scientific paper in the link doesn’t explain how the machine works, just shows test results. So basically this is still unexplained? I WANNA KNOW SO BAAAAAD

Oh and the non-positive on the Kelvin meter, it doesn’t actually mean it was colder than absolute zero. The article actually has a pretty good explanation for it.

tl;dr:

[details=Spoiler]Basically temperature is a measure of how much more disordered a system gets when you add energy to it. Like in a cold gas, particles aren’t moving too fast, so there is a small range of velocities. When you add a certain amount of energy to it, some particles move faster, so the range of velocities becomes larger, so it’s more disordered because each particle is different to a greater extent. In a hot gas, the range of velocities is already large, but when you add the same amount of energy to it as with the cold gas, the range of velocities gets extended by an even larger factor than with the cold gas.

But the setup they did was they limited the maximum energy a particle can have in a gas (idk how lol). If the gas is hot enough, some particles will have the maximum allowable energy, so they move at the maximum allowable velocity. When you add even more energy to the gas, the energy can’t go into the maximum-velocity particles anymore, so it starts to go into the particles at the lower end of the range of velocities. So what happens is the range of velocities becomes smaller when you add energy instead of bigger. That means it gets less disordered when you add energy, so it’s a negative temperature.[/details]

EDIT: Ohhh maybe it’s designed kinda like a laser, so some of the microwaves pass through one side instead of bouncing off it, so you send off a microwave beam in one direction and the thruster moves in the opposite direction? I don’t even know lol, it might not even have anything to do with radiative pressure

EDIT: the spoiler is my tl;dr of the article’s explanation, I wasn’t clear

EDIT: Nobody else posted and I don’t wanna double post so I edited this in

I read something new today, something interesting:

Inventor Develops Synthetic 'Leaf' That Produces Oxygen

Julian Melchiorri, a graduate of the Royal College of Art, claims to have developed a silk leaf that could create oxygen for space travel as well as make the air nicer here on Earth. The leaf was developed in conjunction with a silk lab from Tufts University

The leaf is created from a matrix of protein extracted from silk and chloroplasts, the organelle that allows plants and algae to perform photosynthesis. When provided with light and water, the synthetic leaf allegedly acts just like a real leaf and produces oxygen.

[MechWarrior]

And space has lots of hydrogen just floating in it.
Sustainable!

[pedoviejo]

plans for RAMJETS take advantage of all that goodness.

[forte95]

Did some digging about the impossible thrust engine.

The first design, which was the one that people just laughed at, was this: http://emdrive.com/principle.html

Turns out the first design really was based on radiation pressure.

The thruster had a waveguide material within it that was designed so that the microwaves hitting the front of the thruster were moving faster than the ones hitting the back. The article says that the geometry of the waveguide dictates the effect on the propagation velocity of the microwave. Basically the material tapers and this causes the velocity difference. [details=Spoiler]article doesn’t explain exactly how but it cites a paper, I tried looking for it but I couldn’t find a free pdf off online journals haha, fuck that[/details]

The velocity difference causes a difference in the rate of change of momentum of the front and back of the thrusters. So there is a net rate of change of momentum in one direction: a net force.

I found this link in the original article: http://www.wired.co.uk/news/archive/2014-07/31/nasa-validates-impossible-space-drive

Apparently the design for the thruster that NASA used for testing was slightly different, although it operated on the same concept:

“From what I understand of the Nasa and Cannae work – their RF thruster actually operates along similar lines to EmDrive, except that the asymmetric force derives from a reduced reflection coefficient at one end plate,” he says. He believes the design accounts for the Cannae Drive’s comparatively low thrust: “Of course this degrades the Q and hence the specific thrust that can be obtained.”

I think it’s worth mentioning again that the original design, tested by Chinese scientists, produced about 720 milliNewtons, while the NASA variation produced 30-50 microNewtons. The difference in order of magnitude is 10^4: the NASA variation was around 10 thousand times weaker.

Another thing that interests me is that they say the engine is possibly demonstrating an interaction with the quantum vacuum virtual plasma. I wanna know exactly how, because so far it’s been explained just in terms of radiation pressure

[OGSF]

Thanks to the math thread, I found the science thread:

Theory says that if we lived closer to the Sun then we would age slower than people on Earth. Is this correct?

[pherai]

I think you’re referring to bodies with smaller orbits traveling faster than bodies with larger orbits so relativity says ya, time would slow down for the smaller orbit, but I don’t think you’d notice much of a difference. I think it was one of those Stephen Hawking specials that talked about a ship orbiting closely to a supermassive black hole as a potential time machine.

[pedoviejo]

I think you’re referring to bodies with smaller orbits traveling faster than bodies with larger orbits so relativity says ya, time would slow down for the smaller orbit, but I don’t think you’d notice much of a difference. I think it was one of those Stephen Hawking specials that talked about a ship orbiting closely to a supermassive black hole as a potential time machine.

to elaborate on this, relatively to ourselves a day would feel still feel like 24 hours, but relative to a person outside the earth it’d be several days. this happens as we approach 3 million km per second

[blitzfu]

3 million km per second

Speed of light is about 300,000 km per second (186,000 miles per second).

Speed of light

[forte95]

Yeah and in addition to the slowing-down-time effect due to the planet moving faster, the planet also moves in a more distorted spacetime because it’s closer to the mass of the sun, so basically the time dilation an outside observer will measure is the effect of velocity + the effect of mass on surrounding spacetime

Spoiler

I say mass but energy density is more accurate, I just say mass because things have rest energy just by virtue of having mass plus the phrase “closer to the energy of the sun” is weird

[pedoviejo]

3 million km per second

Speed of light is about 300,000 km per second (186,000 miles per second).

http://en.wikipedia.org/wiki/Speed_of_light

fuck me you be right. It’s been a while and I always scew up scientific notation.

[white_shadow]

That engine sounds crazy!

I’m kind of late to this party but just a little fun fact on how massless particles and particles with mass behave.

Both types of particles have momentum, the difference is particles without mass always travel the speed of light unless hindered by a medium. Particles with mass can never go the speed of light even at the highest agitated states (although particles can be energized enough to travel 99.999999999% the speed of light).

Another good way of explaining temperature in layman terms is that temperature is the excitation or vibration of particles upon receiving energy. Things get hotter because the atoms are moving more rapidly and exchanging various electromagnetic energies, namely infrared radiation. (Like when heated metal glows)

[Don_Barracuda]

Woman takes part in a drug trial to find the best and worst weed

[pherai]

theres a trial id volunteer for, pro bono

[OGSF]

I think you’re referring to bodies with smaller orbits traveling faster than bodies with larger orbits so relativity says ya, time would slow down for the smaller orbit, but I don’t think you’d notice much of a difference. I think it was one of those Stephen Hawking specials that talked about a ship orbiting closely to a supermassive black hole as a potential time machine.

Well, theory states that greater the gravity slower the time